Proteases have long been employed in industry; i.e., in a wide variety of products, including detergents (e.g., laundry detergents), fiber-modifying agents, leather treatment agents, cosmetics, bath agents, food-modifying agents, and drugs. Proteases for detergents are industrially produced in the greatest amounts. Examples of such proteases known heretofore include Alcalase, Savinase (registered trademark; Novozymes), Maxacal (registered trademark; Genencor), Blap (registered trademark; Henkel), and KAP (Kao Corporation).
Protease is incorporated into a laundry detergent for providing the detergent with the ability to degrade dirt, whose main component is protein, deposited on clothing into low-molecular-weight products, thereby promoting solubilization of the thus-degraded products with a surfactant. However, in actuality, such deposited dirt are complex dirt containing, in addition to proteins, a plurality of organic and inorganic components such as sebum-derived lipid and solid particles. Therefore, a demand continues to exist for a detergent exhibiting excellent detergency to such complex dirt.
In view of the foregoing, the present inventors have discovered several alkaline proteases having a molecular weight of about 43,000, which maintain sufficient casein-degrading activity even in the presence of a fatty acid of high concentration and which exhibit excellent detergency to complex dirt containing proteins and sebum; and have previously applied for a patent on the alkaline proteases (see International Publication WO99/18218 pamphlet). These alkaline proteases differ from conventionally known subtilisin, a serine protease derived from bacteria belonging to the genus Bacillus, in molecular weight, primary structure, and enzymological characteristics, and in a property that it has a very strong oxidizer resistance. These alkaline proteases are suggested to be classified into a new subtilisin subfamily (see Saeki, et al., Biochem. Biophys. Res. Commun., 279, 313-319, 2000).
Although the aforementioned alkaline proteases exhibit high detergency to complex dirt containing sebum dirt, etc., demand has arisen for a protease exhibiting further enhanced detergency. Mass production of such a protease exhibiting excellent detergency on an industrial scale requires enhancement of productivity thereof. Examples of the method for such productivity enhancement include a method for improving protease-producing bacteria through mutation; a method for modifying a gene encoding such a protease, or a gene involved in control of expression of the protease, thereby enhancing the amount of the protein to be secreted; and a method for modifying a gene encoding such a protease, thereby enhancing the specific activity of the protease. Thus, the present inventors have conducted studies on modification of genes encoding the aforementioned alkaline proteases, and have discovered a mutant alkaline protease exhibiting enhanced protein secretion ability and specific activity (see JP-A-2004-000122 and 2004-057195).
However, mass production of the enzyme at low cost requires further enhanced production efficiency, and thus the enzyme is required to be secreted in a large amount, not to mention that it has enhanced specific activity and detergency.